A color laser printer employs one set or multiple sets of laser scanning unit (LSU) to irradiate a single beam or multiple beams and has a rotary polygon mirror disposed on a path irradiated by light beams. The rotation angle of the rotary polygon mirror can be driven and controlled by a motor and a corresponding reflection angle configured in accordance with the alignment position of a photosensitive drum, so as to make the photosensitive drum exposed and developed by irradiating the light beams reflected by the rotary polygon mirror thereto while the motor and the LSU receive signal and operate.
The motor structure of the rotary polygon mirror, as shown in FIG. 1 and FIG. 2, includes a metal tube 10, a stator set 20 and a rotor set 30, in which the metal tube 10 is fixedly disposed on a bottom plate 13 and has a bottom lid 11 over the bottom portion of the metal tube 10, and an abrasion-resistant pad is placed inside the bottom lid 11;
the stator set 20 is disposed around the outer periphery of the metal tube 10 (only a silicon steel sheet of the stator set is drawn in FIG. 1); a bearing 14 is disposed inside the metal tube 10, a spindle 34 is enveloped centrally in the shaft hole of the bearing 14 and the bottom end of the spindle 34 is contacted with the abrasion-resistant pad 12 and is held in the shaft hole to rotate;
the rotor set 30 contains a loading disc 31 and a motor housing 32, the top end of the spindle 34 penetrates through the loading disc 31 centrally and is fixed therewith, the motor housing 32 is fixed underneath the loading disc 31 to enclose the stator set 20, and a permanent magnet 33 corresponding to the silicon steel sheet of the stator set 20 is disposed on the inner periphery of the motor housing 32.
The rotary polygon mirror 35 is disposed on top of the loading disc 31 and is fixed by a spring member 40 and a snap ring 36 so as to synchronously rotate with the loading disc 31. The spring member 40 has a center hole 41, and a plurality of spring paws 42 are disposed around the edge of the spring member 40 and obliquely extended in a downward direction, so that the surface of the rotary polygon mirror 35 is urged against by the plural spring paws 42 after the spindle is inserted in the center hole 41. Then, the end of the spindle 34 is clipped and fixed by the snap ring 36 to fix the rotary polygon mirror 35.
When the rotary polygon mirror 35 is assembled with a motor, a weight for securing the stable and balancing effect during high-speed rotation shall be further added and adjusted. As the rotary polygon mirror 35 is every costly, instead of employing a destructive weight-balancing means, regular vendors stick the weight block 351 to the surface of the rotary polygon mirror 35 with adhesive. Whereas, while the motor rotates at a speed of 27000 rpm, the weight block 351 fixed by an adhesive-applying means easily falls off or flings off as a result of gigantic centrifugal force arising from high-speed rotation, thus resulting in the loss of the stable and balancing effect and noise in the operation of color laser printer.